1. Field of the Invention
The present invention relates to a molded plastic product with a pad and a method of manufacturing the same.
2. Description of the Related Art
Molded plastic products having pads are used for various purposes including car interior parts and furniture. The molded plastic product consists of a core and a pad attached to the surface of the core. The pad consists of plastic foam having a given shape and a skin adhering to the plastic foam.
FIG. 13 shows a car instrument panel as an example of the molded plastic products. The panel is made of a pad 80 and a core 90. The pad 80 is attached to a part of the surface of the core 90. Some products have a pad that entirely covers the surface of a core.
FIG. 14 shows a molded plastic product having a pad according to a prior art. The pad 80 is composed of metal inserts 81, plastic foam 82, and a skin 83. The pad 80 is attached to the surface of a core 90 in an afterprocess. Each insert 81 has a pin 84, which is inserted into a hole 91 of the core 90 and is bent or fastened with a clip or screw.
This prior art involves many processes because it must form the pad 80 first and then attach it to the core 90 in a separate process. Since the prior art employs the pins 84 to fix the pad 80 to the core 90, a gap is easily formed between the pad 80 and the core 90, to spoil the external appearance of the product. In addition, the metal inserts 81 make the product heavier.
To solve this problem, a monolithic molding technique of FIG. 15 has been proposed. This technique molds a pad, and at the same time, integrates the pad with a core 95. The core 95 has a pad supporting face 92, a sidewall 93 surrounding the supporting face 92, and a pad housing 94. The core 95 is set on an upper mold 96. A skin 99 of the pad has a side face 97, which is fitted to the pad housing 94, and a back face 98. The skin 99 is set on a bottom mold 100 so that the back face 98 faces the pad supporting face 92. Foam ingredients P like urethane precursors produces foam between the core 95 and the skin 99, to integrate them into one body.
In FIG. 16, the foam produced by the foam ingredients P fills a space between the core 95 and the skin 99. At this time, the pressure generated and increased by rising of the foam ingredients presses the side face 97 of the skin 99 against the sidewall 93 of the core 95, thereby preventing the foam from oozing onto the surface of the skin 99. The tightly fitted sidewall 93 and side face 97 provide the product with a good appearance. The product has no metal inserts, and therefore, is light. In this way, this technique has several advantages. The foam, skin, and core are solidified together due to the self-adhesive property of the foam ingredients.
This prior art, however, has some problems. The side face 97 of the skin 99 has low rigidity because of a free end 101. The side face 97 is easily deformed or corrugated during storage or on the bottom mold 100. Once the side face 97 is deformed, it causes a gap 102 with respect to the sidewall 93 as shown in FIG. 17. Then, the foam ingredients P may ooze onto the surface of the skin 99, to spoil the appearance of the product or cause unfilled spots in the pad. The deformed side face 97 will not restore to an original shape even if the skin 99 is heated. This problem is difficult to solve.
Powder slush molding is easy to control thickness of a skin. This technique may be employed to thicken the side face of a skin and improve the rigidity thereof. This technique forms a skin on the inner face of a slush mold and takes off the skin from the mold by pulling a free end of the side face of the skin. At this time, the side face is easily corrugated. Accordingly, this technique is insufficient to prevent a deformation of the side face of the skin.
When molding a large plastic product such as an instrument panel having a pad, depending on the position of injecting foam ingredients with respect to the large product, or because a gap between a core and a skin of the product is not uniform, the foam ingredients can flow irregularly to unevenly press the side face of the skin against the sidewall of the core. This results in collecting to pressure generated and increased by rising of the foam ingredients to the gap and leaking the foam ingredients through the gap onto the surface of the skin.
There is another problem that the quality of the skin deteriorates during use and the skin shrinks to peel the side face of the skin off the foam.